Based on our long ( \sim 300 ks ) 2007 XMM-Newton observation of the Seyfert galaxy NGC 1365 , we report here on the spectral and timing behaviour of two ultraluminous X-ray sources , which had previously reached isotropic X-ray luminosities L _ { X } \approx 4 \times 10 ^ { 40 } erg s ^ { -1 } ( 0.3 – 10 keV band ) .
In 2007 , they were in a lower state ( L _ { X } \approx 5 \times 10 ^ { 39 } erg s ^ { -1 } , and L _ { X } \approx 1.5 \times 10 ^ { 39 } erg s ^ { -1 } for X1 and X2 , respectively ) .
Their X-ray spectra were dominated by power-laws with photon indices \Gamma \approx 1.8 and \Gamma \approx 1.2 , respectively .
Thus , their spectra were similar to those at their outburst peaks .
Both sources have been seen to vary by a factor of 20 in luminosity over the years , but their spectra are always dominated by a hard power-law ; unlike most stellar-mass BHs , they have never been found in a canonical high/soft state dominated by a standard disk .
The lack of a canonical high/soft state seems to be a common feature of ULXs .
We speculate that the different kind of donor star and/or a persistently super-Eddington accretion rate during their outbursts may prevent accretion flows in ULXs from settling into steady standard disks .